refactor: no comments left - one-line module docstrings, contracts on public fields only; jobs/job.py; example config and README

src/beaver_gateway/frontends/sse.py

@@ -29,10 +29,8 @@ async def events_with_heartbeat(
 ) -> AsyncIterator[Any]:
     """Pass ``events`` through, yielding ``None`` after ``interval`` seconds of silence.
 
-    One in-flight ``__anext__`` task is reused across timeouts: a second
-    consumer on the same async generator raises ``RuntimeError``.
-    Cancellation of the outer scope cancels that task instead of leaving
-    it dangling.
+    Only one consumer may iterate the result at a time; cancelling the
+    outer scope cancels the in-flight upstream fetch instead of leaking it.
     """
     src = events.__aiter__()
     next_task: asyncio.Task[Any] | None = None